Sequencing And Phelogenetic Analysis Of Hypervariable Region Of Infectious Bursal Disease Virus VP2 Gene

Infectious bursal disease(IBD) is a highly touched infectious disease caused by Infectious bursal disease virus (IBDV) . Immunosuppression is caused when chichens are infected by IBDV.The double stranded RNA(dsRNA) genome, which is divided over two segments, is packed within a capsid. VP2 gene was located in the larger genome segment A. VP2 protein was the main structural protein and protective antigen of IBDV. A hypervariable region (AA206-AA305) including a seven-peptide sequence (S-W-S-A-S-G-S) and two hydrophilic regions (â… (AA212-AA224),â…¡(AA314-AA324)) existed in the VP2 amino acid sequence. The serine residues in the seven-peptide sequence played an important role in the virulence of IBDV. The hydrophilic regions were very important for antigenic determinants of IBDV. Besides, IBDV strain would become very virulent (vvIBDV) when some amino acid residues changed (Q249K,G254S,N279D,T284A). The hypervariable region of VP2 gene of six isolates (Y3,P2G,P8G,SZ,Y5 and W04) from Jiangsu province was amplified by RT-PCR . six segments were cloned into pMD18T vector ,sequenced and analyzed. The results indicated that the six isolates were closely related with each other and had very high similarity with D6984 strain isolated from Dutch (99.0%) and other vvIBDV (more than 97.8%). Their amino acid sequences had the same characteristics with vvIBDV amino acid sequences. Based on 26 IBDV sequences, phylogenetic tree was constructed. The six isolates and vvIBDVs isolated from Europe and Japan were in the same branch. So it was suggested that the six isolates (Y3,P2G,P8G,SZ,Y5 and W04) isolated from Jiangsu province were vvIBDV.